Process and catalyst for treating combustion exhaust gas

ABSTRACT

THE EXHAUST GAS FROM INTERNAL COMBUSTIO ENGINES OR THE LIKE IS TREATED TO CONVERT HARMFUL OR POLLUTANT COMPONENTS SUCH AS NITROGEN OXIDES, CARBON MONOXIDE AND UNBRUNED HYDROCARBONS TO INNOCUOUS COMOUNDS, BY CONTACTING THE WXHAUST GAS WITH A CATALYST COMPOSITION CONTAINING NICKEL, COBALT AND MANAGNESE IN CATALYTICALLY EFFECTIVE AMOUNTS, DEPOSITED ON A CARRIER SUCH AS ALPHA ALUMINA.

United States Patent O 3,701,822 PROCESS AND CATALYST FOR TREATING COMBUSTION EXHAUST GAS John S. Negra, South Plainfield, and Abe Warshaw, Matawan, N.J., assignors to Chemical Construction Corporation, New York, N.Y. No Drawing. Filed June 11, 1970, Ser. No. 45,576 Int. Cl. B01d 53/54 U.S. Cl. 423213 3 Claims ABSTRACT OF THE DISCLOSURE The exhaust gas from internal combustion engines or the like is treated to convert harmful or pollutant components such as nitrogen oxides, carbon monoxide and unburned hydrocarbons to innocuous compounds, by contacting the exhaust gas with a catalyst composition containing nickel, cobalt and manganese in catalytically elfective amounts, deposited on a carrier such as alpha alumina.

BACKGROUND OF THE INVENTION Field of the invention-The invention relates to the elimination of deleterious compounds such as nitrogen oxides, carbon monoxide and residual hydrocarbons, which are present in the exhaust gas from internal combustion engines such as diesel engines or gasoline-burning automobile engines, so as to prevent the discharge of these noxious components into the atmosphere, and thereby prevent air pollution. The term internal combustion engine will be understood to encompass other types of combustion devices and engines such as gas turbines or the like.

Description of the prior art.-In recent years it has been recognized that the exhaust gas discharged from internal combustion engines is a serious source of air pollution, especially in metropolitan areas. In some cases, a so-called smog is generated due to atmospheric inversions and accumulation of such exhaust gases in the atmosphere. Recent attempts to prevent such air pollution have concentrated on the destruction or elimination of noxious components by catalysis, especially by admixture of secondary air into the exhaust gas followed by catalytic oxidation of residual hydrocarbons, carbon monoxide, etc., in various types of apparatus specially designed for this purpose. Improvements in active catalytic agents for this function are described in U.S. Pats. Nos. 3,053,773; 3,429,656; 3,316,057, 3,398,101; 3,477,893; 3,476,508 and 3,493,325. A catalytic agent containing nickel or cobalt, and manganese, for the catalytic reaction of naphtha with steam to produce methane, is described in U.S. Pat. No. 3,466,159.

SUMMARY OF THE INVENTION In the present invention, it has been determined that a catalytic agent containing small but catalytically effective amounts of a synergistic combination of nickel, cobalt and manganese deposited on a carrier is highly etfective in treating exhaust gases from internal combustion engines or the like, in order to reduce nitrogen oxides to nitrogen, and also oxidize carbon monoxide and vaporous hydrocarbons to carbon dioxide and water vapor. The manganese will generally be present as manganese oxide, however the nickel and cobalt may be at least partially present as reduced oxides or in the metallic state. In the description and claims infra, catalyst compositions will refer to metallic components in terms of equivalent oxide content, however the metals such as nickel or cobalt may be partially present in actuality as other compounds or as reduced elemental metals or in the metallic state. However, equivalent oxide composition is reported on analysis, as is I 3,701,822 Patented Oct. 31, 1972 Ice.

customary in the art. Similarly, the manganese content may actually be present in practice at least partially as the sub-oxide, however for purposes of analysis and composition terminologythe manganese content is reported as equivalent manganese dioxide.

The exhaust gas is passed through a catalyst bed or mass containing nickel oxide, cobalt oxide and manganese dioxide. It has. been determined that highly beneficial results are thereby attained, in terms of removal of nitrogen oxides from the exhaust gas by reduction, and removal of carbon monoxide and hydrocarbon vapors by oxidation, due to the synergistic action of the three metallic constituents in the catalyst. The process is carried out most effectively with a catalyst bed having a composition containing (by weight) in the range of from about 6% to 12% equivalent nickel oxide, 1% to 5% equivalent cobalt oxide and 0.5% to 3% manganese dioxide. These catalytic agents will be deposited on a suitable carrier such as alumina,-preferably as the alpha form of alumina, or silica, kaolin or magnesia, in some cases together with a suitable binder. In most instances the invention will be practiced with two catalyst beds in series, in which series flow of exhaust gas takes place through the two beds and air which may be preheated is injected into the partially reacted exhaust gas between beds. A typical apparatus for carrying out the process is described in U.S. patent application No. 33,359 filed Apr. 30, 1970 now U.S. Pat. No. 3,656,915. A temperature level generally in the range of 300 C. to 800 C. will usually be provided in the catalyst beds during reaction, however the invention may be practiced at lower temperatures, such as when starting a cold automobile engine, or at temperatures above 800 C.

It is an object of the present invention to provide an improved process and catalyst for treating exhaust gases from internal combustion engines to remove noxious components.

Another object is to prevent air pollution due to the discharge of exhaust gas from internal combustion engrnes.

A further object is to provide an improved process and catalyst for catalytically reducing nitrogen oxides and oxidizing carbon monoxide and hydrocarbon vapor in the exhaust gas from an internal combustion engine.

An additional object is to provide a synergistic combination of nickel, cobalt and manganese in a catalyst composition for treating the exhaust gas from internal combustion engines.

DESCRIPTION OF THE PREFERRED EMBODIMENT AND EXAMPLES A catalyst composition was prepared in accordance with the present invention. The catalyst was prepared by double impregnation of an alpha alumina (9%") carrier with the nitrate salts of the catalytically active metals: Nickel (Ni), cobalt (Co) and manganese (Mn). Some ammonium nitrate was also added to assist in the activation procedure. The nitrates are decomposed at 210 C. to 230 C. for a period of at least 24 hours, and preferably 48 hours. Activation is completed by reducing the catalyst at 400 C. to 450 C. with hydrogen. Catalyst compositios were prepared or formulated in a series of tests with equivalent nickel oxide content varying from 6% to 12% by weight, equivalent cobalt oxide content varying from 1% to 5% by weight, and manganese dioxide varying from 0.5% to 3% by weight. Following are the test results.

The performance of the Ni- Co-Mn catalyst of the present invention was tested with synthetic exhaust gas mixtures simulating automobile exhaust gases using nonleaded gasoline, and the catalyst performance was evaluated.

Table II.-Com-position range of the test gas Percent CO, 12-13 Percent CO 2-4 Percent 0-0.6 P.p.m. C H 150-1500 P.p.m. NOx 1000-2500 Percent H O ll-13 Percent N Remainder In the operational procedures, the activity of the catalyst was tested in a. two stage ceramic tube reactor. Heat was maintained in the upper portion of the tube with an electric tube furnace and in the lower part by an electric heating tape. The test gas was preheated in the lower part of the tube and mixed with additional air just before entering the second stage of the reactor which was separated from the first stage by a 7.6 cm. bed of inert Alundum spheres. The first stage of the reactor consisted of between 5.1 and 6.35 cm. of the catalyst pellets and the second stage consisted of from 3.2 to 5.1 cm. of the same material. Reaction temperatures ranged from 300. C. to 800 C. and space velocities from 8000 to 20,000 v./v./hr.

Table 1II.--Stability test: Ni-Co-Mn catalyst Space velocity, v./v./hr. (saturated 50 C.) 9600 Total reaction time (hrs.) 6

Temp. at start of test, C. 500 Maximum temp. reached, C. 800 Temp. at end of test, C 350 Inlet NOx content (P.p.m.) 1640 Exit NOx at all temps. (p.p.m.) 10 Crush strength as completion ..lb' 60 It is evident from thet results of Table I II that substantially all of the nitrogen oxides (NOx) are removed from the test 'gas by thecatalytic action of the present catalyst, and that the final crush strength at completion is at an acceptable level.

EXAMPLE II- Two-stage reactor. performance was tested with the catalyst of Example I, prepared for pollution control in automobile mufllers.

Table IV.Simulated automobile mufiler Space velocity, v./v./hr. (saturated 50 C.) 10,600 Gas temp. inlet to 1st stage C 320-335 Gas temp. exit to 2nd stage C 415-580 Additional air to 2nd stage ....m1./min.... 800

Gas analysis:

Exit gas Feed test: analysis Component gas range Percent:

002 13.0 14.4-14.6 CO 2.3 0-0 02 .0.6 0.8-1.8 P.p.m.

CeHil 49 1-40 NOx 1,040 50-90 Duration oftests averaged 4 hours. The catalyst crush strength when charged to reactor was 60# (pounds), crush strength after four hour tests was When the above test gas was reacted without water saturation, the

The Ni-Co-Mn catalyst of the present invention as prepared per Example I was tested for effectiveness versus a copper-cobalt catalyst, which contained 6.90 to 10.30% C110, and 0.7-8 to 1.54% C0 0 Following are the comparative test results, in a two-stage reactor.

TABLE V.COMPARISON OF CATALYST PERFORMANCE Nl-Co-Mn catalyst Cu-Co catalyst Inlet gas Exit gas Inlet gas Exit gas 1, 640 105 1, 350 215 1. 97 0 2. 84 0 1, 140 0 1, 450 22 emp., C..--- 425 765 415 770 02 in exit gas (percent) 1. 6 1. 0

The superior effectiveness of the Ni-Co-Mn catalyst of the present invention is evident from Table V.

EXAMPLE IV.COMMERCIAL SCALE TESTS As a result of favorable results obtained in bench scale tests, it was concluded that the Ni-Co-Mn catalyst of the present invention exhibited greater activity than standard catalysts in reducing the quantityof gaseous pollutants in simulated auto exhaust gases. The catalyst was therefore made in sufficient amounts to fill auto mufllers for performance evaluation by a major automobile manufacturer. A total of pounds of commercial alpha alumina catalyst carrier was used to prepare four batches of the Ni-Co-Mn catalyst. Each batch was analyzed and checked for activity. The activity in each case was found to be equal to the small scale preparations previously tested although the metals analysis showed some variation. The composition range of the catalysts is shown in Table VI.

Table VI.Composition range of catalysts prepared for commercial auto mufilers Percent nickel as NiO 7.64-9.86 Percent cobalt as C0 0 2.01-2.60 Percent manganese as MnO 0.80-1.65

Percent aluminum as A1 0 85.89-89.55 Crush strength in pounds 50-70 TABLE VIL-PERFO RMANCE 0F Ni-C o-Mn CATALY S T AU TO MUFFLE R S The reactor was a two-stage tube with air injected into the second stage. Space velocity (v.v./hr.) was 10,600, saturated at 40 C. to 50 C. Following is a summary of pollutants removal.

Table VlIL-Summary of pollutants removal, commercial scale test Carbon monoxide percent Nitrogen oxides do 95.8 Hydrocarbons as C H do 94.5 Average inlet gas temp C 356 Average exit gas temp C-.. 522

In an associated heat stability test, the Ni-Co-Mn catalyst was reacted for 6 hours. The first hour, the temperature did not exceed 500 C. For 4 hours the temperature was maintained between 500 C. and 800 C. Near the The tests were made on a conventional car engine. The exhaust gases issuing from the standard mufiier were analyzed and compared to the analysis of the gases when the catalytic mufiler was installed.

All data was recorded when the exit gases reached temperatures between 350 C. and 400 C.

TABLE IX.-SINGLE STAGE PERFORMANCE (HOT CYCLES) Standard Catalytic Hydrocarbons (p.p.m.) 65 19 Carbon monoxide (percent) 0. 54 0.09 Nitrogen oxides (p.p.m.) 460 176 The results show that the hydrocarbon and carbon monoxide emissions would pass the projected 1980 emis sion standards.

The nitrogen oxides would pass the 1975 emission standard.

TABLE X.TWO STAGE MUFFLER PERFORMANCE (HOT CYCLES) Standard Two-stage muflier muifler Hydrocarbons (p.p.m.) 126 13 Carbon monoxide (percent)- 5. 3 0. 4 Nitrogen oxides (p.p.m.) 100 The nitrogen oxides emission was slightly higher than the projected 1980 standard. The hydrocarbon and carbon monoxide emissions would meet the 1980 specifications.

We claim:

1. A process for the treatment of exhaust gas from an internal combustion engine which comprises contacting an exhaust gas with a solid catalyst containing nickel in the range of about 6% to 12% by weight of equivalent nickel oxide, cobalt in the range of about 1% to 5% by weight of equivalent cobalt oxide, and manganese in the range of about 0.5% to 3% by weight of manganese oxide, deposited on an alpha alumina carrier, said nickel and cobalt being at least partially present in said catalyst in the form of elemental metals derived from reduced oxides.

2. The process of claim 1, in which said exhaust gas is contacted with said catalyst at a temperature in the range of 300 C. to 800 C.

3. The process of claim 1, in which said exhaust gas is contacted with said catalyst in two catalyst bed stages, with series flow of exhaust gas through both stages, and air is injected into the partially reacted exhaust gas between stages.

References Cited UNITED STATES PATENTS 3,214,236 10/1965 Weisz 232 E 3,397,154 8/1968 Talsma 232 E X 3,086,839 4/1963 Bloch 232 E 3,230,182 1/1966 Stiles 232 E X 3,228,746 1/1966 Howk et al. 232 E 1,345,323 6/1920 Frazer 232 E FOREIGN PATENTS 989,728 4/ 1965 Great Britain 232 E OSCAR R. VERTIZ, Primary Examiner G. O. PETERS, Assistant Examiner US. Cl. X.R. 252471 

